Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Plural component system comprising a - group i to iv metal...
Reexamination Certificate
1999-04-07
2001-01-30
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Plural component system comprising a - group i to iv metal...
C502S103000, C502S117000, C502S155000, C502S158000, C502S167000, C526S127000, C526S132000
Reexamination Certificate
active
06180552
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to neutral pyrazolyl, triazolyl, and tetraazolyl-containing ligands (“azacyclic” ligands) and transition metal complexes that contain them. The complexes are valuable procatalysts for organic reactions, particularly for olefin polymerizations.
BACKGROUND OF THE INVENTION
The chemical industry uses a wide variety of transition metal complexes as catalysts for organic reactions. Polyolefin manufacture is a good example. While conventional Ziegler-Natta catalysts continue to dominate the industry, highly active metallocene or single-site catalysts that give new polymers with narrow molecular weight distributions, low densities, and good comonomer incorporation are emerging.
Transition metal complexes used to polymerize olefins are normally non-zero-valent metals (e.g., Ti
4+
, Zr
4+
, Sc
3+
) surrounded by anionic ligands (e.g., chloride, alkyl, cyclopentadienyl) that satisfy the valency of the metal and often improve the solubility of the catalyst in the reaction medium. The anionic ligands can dramatically impact catalyst activity and polymer properties.
Neutral, multidentate ligands have been used only sparingly in preparing the transition metal complexes useful as precursors for metallocene or single-site polyolefin catalysts. For example, 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn) has been used to prepare (tmtacn)MCl
3
complexes of scandium, chromium, and rhodium (see, for example, Wang et al.,
J. Am. Chem. Soc.
119 (1993) 6999); derivatives of these complexes catalyze olefin polymerizations. Another example is 1,4,7-trithiacyclononane (ttcn), from which (ttcn)RhCl
3
has been prepared (S. Timonen et al.,
J. Mol. Catal. A.,
111 (1996) 267). Because of their complexity, high cost, and synthetic challenge, such ligands have not been widely pursued. While more accessible neutral ligands (such as 1,2-bis(diphenylphosphino)ethane) exist, these have not generally provided significant advantages for metallocene and single-site catalysts.
A potentially viable route to neutral, multidentate ligands reacts three equivalents of pyrazole with chloroform in the presence of a base to give a tris(pyrazolyl)methane. This method is economically attractive because a variety of pyrazoles can be made by reacting acetylacetones with hydrazine. Unfortunately, carbene formation complicates the product mixture and reduces the yield of the desired tris(pyrazolyl) compound.
Anionic tris(pyrazolyl)borate ligands are known. U.S. Pat. No. 5,504,049, for example, reacts VOCl
3
with potassium tris(pyrazolyl)borate to make a complex that polymerizes ethylene in the presence of an activator such as MAO. In addition, one tris(pyrazolyl)silane compound is known: S. Vepachedu et al. (
Acta Cryst.
C51 (1995) 423)) reported the crystal structure of tris(3,5-dimethylpyrazolyl)methylsilane.
In sum, new neutral, multidentate ligands are needed. Particularly valuable ligands would be easy to synthesize from readily available starting materials. Preferably, the ligands could be made in high yields without complicating side reactions such as carbene formation. Ideally, the ligands would be valuable for making new transition metal complexes useful as procatalysts for olefin polymerization.
SUMMARY OF THE INVENTION
The invention is a new class of neutral, multidentate ligands. The ligands have the general formula: R
a
—A—(L)
b
where R is hydrogen or C
1
-C
30
alkyl, aryl, or aralkyl, A is silicon, tin, germanium, or lead, each L is independently a substituted or unsubstituted pyrazolyl, triazolyl, or tetraazolyl group, a=0 to 2, b=2 to 4, and a+b=4, with the proviso that when R=methyl, A is silicon, and a=1, then L is not a 3,5-dimethylpyrazolyl group.
The invention includes transition metal complexes which comprise a Group 3 to 10 transition or lanthanide metal (M), one or more anionic or neutral ligands in an amount that satisfies the valency of M, and the neutral, multidentate ligand described above. The invention also includes catalysts for olefin polymerization; these comprise the transition metal complexes and an activator such as MAO or a borate salt. Finally, the invention includes an olefin polymerization process that uses the catalysts.
I surprisingly found that neutral, multidentate ligands based on Group 14 elements (silicon, tin, germanium, or lead) and pyrazolyl, triazolyl, or tetraazolyl groups are easy to synthesize and purify. Moreover, the ligands readily react with Group 3 to 10 transition and lanthanide metals to give complexes that are potentially valuable for a wide range of organic transformations, including olefin metathesis, isomerization, oligomerization, and the like. In particular, the complexes react with common activators such as alumoxanes or borate salts to provide excellent single-site catalysts for olefin polymerization.
DETAILED DESCRIPTION OF THE INVENTION
The neutral, multidentate azacyclic ligands of the invention have the general formula R
a
—A—(L)
b
. In the formula, A is a Group 14 element, excluding carbon. In other words, A can be silicon, germanium, tin, or lead. Silicon is preferred. R is hydrogen or a C
1
-C
30
alkyl, aryl, or aralkyl group. Preferably, R is hydrogen or a C
1
-C
5
alkyl group. Each L is independently a pyrazolyl, triazolyl, or tetraazolyl group; a=0 to 2, preferably 1 to 2; b=2 to 4, preferably 2 to 3; and a+b=4.
By “pyrazolyl,” we mean a group with the structure:
in which any of the three ring carbons is unsubstituted (i.e., has one hydrogen) or is substituted with R
1
, R
2
, and/or R
3
, each of which may be independently a hydrocarbyl, halide, alkoxide, dialkylamino, nitro, or similar group. Two adjacent hydrocarbyl groups may be joined to form a cyclic structure, as in indazole or tetrahydroindazole. The pyrazolyl groups are sigma-bonded to the silicon, tin, germanium, or lead atom through the 1-nitrogen. Unsubstituted and hydrocarbyl-substituted pyrazolyl groups are preferred.
Similarly, triazolyl ligands have the following structures:
in which R
1
and R
2
are defined as above.
A tetraazolyl ligand has the following structure:
in which R
1
is defined as above.
Suitable neutral, multidentate ligands include, for example, bis(pyrazolyl)dimethylsilane, bis(pyrazolyl)methylphenylsilane, bis(pyrazolyl)diphenylsilane, bis(pyrazolyl)bis(dimethylamino)silane, bis(pyrazolyl)silacyclobutane, bis(pyrazolyl)silacyclopentane, bis(3,5-dimethylpyrazolyl)dimethylsilane, bis(indazole)dimethylsilane, bis(4-chloropyrazolyl)dimethylsilane, bis(4-methylpyrazolyl)dimethylsilane, bis(3,5-trifluoromethylpyrazolyl)dimethylsilane, tris(pyrazolyl)methylsilane, bis(pyrazolyl)methylsilane, tris(3-methylpyrazolyl)methylsilane, tetrakis(pyrazolyl)silane, bis(triazolyl)dimethylsilane, bis(benzotriazolyl)dimethylsilane, tris(benzotriazolyl)methylsilane, bis(tetraazolyl)dimethylsilane, tris(tetraazolyl)methylsilane, tris(pyrazolyl)methyltin, tris(3,5-dimethylpyrazolyl)germane, tris(pyrazolyl)methylgermane, tetra(pyrazolyl)lead, tetra(3,5-dichloropyrazolyl)silane, and the like, and mixtures thereof. Particularly preferred are bis and tris(pyrazolyl)alkylsilanes and bis and tris(3,5-disubstituted pyrazolyl)alkylsilanes.
The neutral, multidentate ligands are easy to prepare. The azacycles (e.g., pyrazole, 3,5-dimethylpyrazole, benzotriazole, tetrazole, and the like) are often commercially available. In one convenient preparation, the azacycle is deprotonated by reacting it with a strong base such as n-butyllithium in an inert solvent (e.g., ether). Evaporation of solvent gives the alkali metal salt. Two to four equivalents of this salt are then reacted with a Group 14 compound, preferably one having an equivalent number of good leaving groups (e.g., three moles of azacycle salt and one mole of methyltrichlorosilane) to produce the neutral, multidentate ligand. The workup usually consists of dissolving the reaction products in a solvent (hydrocarbon or halogenated hydrocarbon, e.g.), filtering to remove alkali metal salts, and recrystallizing
Bell Mark L.
Equistar Chemicals L.P.
Pasterczyk J.
Schuchardt Jonathan L.
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